(a) Field of the Invention
The present invention relates to an ultrasonic coupling agent of a low viscosity for use between an ultrasonic probe and skin surface of a patient, during ultrasonic diagnosis.
(b) Description of the Prior Art
In ultrasonic diagnosis, an ultrasonic probe is brought into contact with the skin surface of a patient, an ultrasonic wave is emitted from the probe, and a wave reflected by body tissue is detected to diagnose the presence of abnormal tissue or the pulsation of blood flow. Ultrasonic diagnosis has been in widespread use in many medical institutions or hospitals.
An ultrasonic coupling agent is required between the probe and the skin surface of the patient to prevent attenuation of the ultrasonic wave or abnormal reflection thereof. Examples of the ultrasonic coupling agent are water, animal/vegetable oil such as olive oil and castor oil, glycerin, or an aqueous solution of a natural or synthetic polymer such as guar gum and polyvinylalcohol. Such an ultrasonic coupling agent is used in the form of a solution, gel, or sheet. A solution-type ultrasonic coupling agent is applied directly to the skin surface of the patient. A gelatinous or sheet-like ultrasonic coupling agent is applied directly to the skin surface so that a gap between the skin surface and the probe is not formed. The ultrasonic coupling agent coated directly on or adhered to the skin surface must not cause discomfort to the patient or affect the skin in any way. In addition, the ultrasonic coupling agent must be easily removed after diagnosis.
However, the solution-type ultrasonic coupling agent has low ultrasonic transmissivity, shows a tendency to adhere to the skin surface, is unable to form a uniform ultrasonic coupling agent layer due to oil on the skin surface, and is subject to irregular coating due to the repelling action of the skin. On the other hand, in animal/vegetable oil or glycerin-ethylene glycol agents, the stickiness of the coupling agent causes discomfort to the patient. Removal of the ultrasonic coupling agent after diagnosis is cumbersome and time-consuming, thus being even more discomforting to the patient.
When a gelatinous or sheet-like ultrasonic coupling agent is adhered to the skin surface, a satisfactory ultrasonic transmissivity cannot be guaranteed. In addition, ultrasonic attenuation and reflection of the wave from the contact portion between the skin surface or the probe and the agent is conspicuous. If the body part to be examined is a curved portion such as a mammary gland or the throat area covering the thyroid gland, adhesion between the skin surface and the sheet-like ultrasonic coupling agent is unsatisfactory.
In ultrasonic diagnosis of a curved body portion (e.g., a mammary gland or the throat area covering the thyroid gland) or a three-dimensional skin surface (e.g., a suture line following surgery), a water bag filled with deaerated water is used in between the body portion and the probe. Alternatively, the probe is inserted in a rubber or plastic water bag and is brought into contact with the portion to be examined. In either case, the entire skin surface must be brought into contact with the water bag so as not to allow the formation of air bubbles. For this purpose, an ultrasonic coupling agent must be used between the water bag and the skin surface, with the attendant discomfort to the patient. Thus, the problems posed by the conventional ultrasonic coupling agents as described above have not yet been solved.
In addition, the conventional ultrasonic coupling agents do not have optimal properties such as wettability and slidability. Therefore, a great demand has arisen for an ultrasonic coupling agent which solves all the conventional problems. Since ultrasonic diagnosis is used for many different patients, it is very important not to transmit infectious diseases from one patient to another. Although it is desirable to use a disinfected or sterilized probe, since it is to be brought into direct contact with a patient's skin, it is difficult to perform this due to probe cost and in the interest of workability. Since ultrasonic diagnosis is an easy and noninvasive method of examination, it is in widespread use for a large number of patients. Because of this, although disinfection/sterilization of the probe before each examination is necessary, it cannot be actually performed due to the above-mentioned difficulties.